1. Field of the Invention
The present invention relates to a light emitting diode (LED), and more particularly, to an LED package structure having plural LED chips so that a better spatial color uniformity can be obtained and claims benefit of Taiwan 098222141 filed Nov. 26, 2009.
2. Description of Related Art
Referring to FIG. 1, a cross-sectional view illustrating a conventional LED package structure, the LED package structure comprises a heatsink slug 1, a positive-electrode frame 2, a negative-electrode frame 3, and an LED module 4. The heatsink slug 1 is, at its top, formed with a cup-like recess 5 for bonding the LED module 4, where a plane for loading the LED module 4 is referred to as a “die-bonding plane 6.” The LED module 4 may be a single or plural electrically-connected LED chips, which, through two gold wires (not shown), can be electrically connected with the positive-electrode frame 2 and the negative-electrode frame 3.
There is a fluorescent colloidal layer 7 covering on the LED module 4, and that an insulating frame 8 envelopes and fixes part of the heatsink slug 1 and of the frames 2,3.
Taking a widely-applied LED as an example, the LED module 4 may be a blue-light LED chip, and that the fluorescent colloidal layer 7 may be a yellow fluorescent colloidal layer contained yellow phosphor (not shown). The theory for its function resides in using a short-wavelength blue-light to excite the fluorescent powder for emitting a longer-wavelength yellow light, which then are mixed into a white light due to complement of colors.
However, there is a potential problem in the above-mentioned conventional LED package structure, namely, when an LED chip and a fluorescent powder emit lights of different colors which are distributed non-uniformly, then a phenomenon of color variation will occur where colors are non-uniform. Since the LED chip relates to an extended plane light source, a normal-direction component of blue light (as shown by arrow P) is greater than the components of other directions. This makes it necessary for the fluorescent colloidal layer 7 covering on the normal-direction component thicker than the components of other directions, so that a better spatial color uniformity can be obtained. The method for this achievement resides in applying the theory of surface tension such that when a silicone gel is formed on the LED chip (volume-dispensing method), a curved and convex gel surface can be formed.
Nevertheless, in case a dimension of the cup-like recess 5 becomes greater to a certain extent (for example, in an occasion where plural LED chips are received therein), the known volume-dispensing method can hardly form an ideal curved and convex contour on the fluorescent colloidal layer 7, but rather a slightly curved surface. Under such circumstances, the fluorescent colloidal layer 7 covering on the normal-direction component, instead, becomes thinner than the components of other directions. This will result in a great amount of normal-direction blue light penetrating the fluorescent colloidal layer 7. Therefore, a higher color temperature occurs in the normal direction, while a lower color temperature at two sides and surroundings, and as such, a tint phenomenon is produced.